1. Field of the Invention
The invention relates to a cold gas generator for an airbag system, comprising a storage device, whose interior is filled with a gas under pressure, comprising a gas outlet opening closed in the rest state, and comprising an opening mechanism for opening the gas outlet opening when needed and for filling an airbag with the gas.
2. Description of the Related Art
Known airbag systems, as they are used in the automobile industry and as they can be used in the railway industry as well as in the airplane industry, are comprised essentially of an airbag which is folded in the rest state and can be filled with the gas when needed; a gas generator which provides the gas for filling the airbag; and a triggering device which initiates the filling of the airbag in the case of an accident when a certain limit value is surpassed. A so-called cold gas generator has a storage device filled with a gas under pressure and a gas outlet opening which is closed in the rest state and can be opened by an opening mechanism when needed for filling the airbag.
Increasing requirements with respect to safety technology demand the development of increasingly more complex airbag systems. For example, for protection against a combined frontal and side impact, the arrangement of a front airbag and a side airbag can be expedient. The aforementioned side airbag can be developed as a system of, for example, three individual airbags wherein each individual airbag is matched with regard to its properties to the body parts to be protected. The required plurality of gas generators is expensive and thus prevents the broad use of such modern safety technology. A temporally precisely coordinated filling of the individual airbags in an accident situation is difficult.
It is an object of the present invention to provide a cold gas generator of the aforementioned kind which enables the use of airbag systems with improved coordination and reduced cost expenditure.
In accordance with the present invention, this is achieved in that the interior of the storage device is divided into at least two partial chambers, wherein the partial chambers have correlated therewith a gas outlet opening for filling several separate airbags, respectively, and wherein the gas outlet openings can be actuated together by the opening mechanism.
By dividing the interior of the storage device into at least two partial chambers and by correlating a gas outlet opening with a partial chambers, respectively, several airbags can be filled from one storage device. By arranging an opening mechanism such that it actuates the gas outlet openings together and thus fills the separate airbags, it is ensured that with a defined triggering signal all connected airbags can be filled in a temporally adjusted way and thus provide a coordinated protective system. Moreover, it is achieved in this way that for a system of several airbags only one storage device and only one opening mechanism are required; this lowers the investment costs. Optionally, the corresponding storage device provided with several chambers can be mounted as standard equipment in a vehicle, with only a minimum number of individual airbags being connected thereto. With minimal additional expenditure, additional airbags, ordered by the customer, can be connected without the cold gas generator itself having to be modified, exchanged, or supplemented with additional cold gas generators.
In a preferred embodiment, the storage device of the cold gas generator comprises a cylindrical center part which extends along a longitudinal axis and which has a longitudinally movable piston arranged therein. The piston forms a partition for dividing the interior into two partial chambers and, in its rest position, closes a gas outlet opening of one of the two partial chambers. With this arrangement, only a simple opening mechanism must be provided which acts only on one gas outlet opening. When opening this gas outlet opening, the gas pressure in one of the partial chambers drops and, as a result of this, the piston is moved in the direction of the longitudinal axis of the storage device and thus releases the additional gas outlet opening.
Particularly in the case of an arrangement with several pistons, which separate a partial chamber from one another, respectively, and which close in the rest position a correlated gas outlet opening, respectively, several airbags of an airbags system can be filled in a simple and coordinated way because only a single opening mechanism must be actuated. In this situation, a connection of the pistons with one another by means of a piston rod is expedient. In this way, the precision of the temporal adjustment of the individual opening processes is improved. The piston rods are preferably of a tubular design because, in this way, a high buckling stability can be obtained while a minimal weight is ensured at the same time. The high buckling stability is required as a result of the occurring high gas pressures. At the same time, a minimal total mass of the moving parts is desirable because high triggering speeds in the range of a few milliseconds are required.
A simple and effective opening mechanism is realized by providing a sealing disk closing off a gas outlet opening provided at the end face of the storage device, wherein the sealing disk has a rated break-off location and is supported by a support element. For example, a pyrotechnical actuator can laterally or rotatingly move, when needed, the support element such that the sealing disk is no longer supported. The rated break-off location is dimensioned or selected such that in the unsupported state of the sealing disk it is destroyed by the gas pressure acting on it and the sealing disk thus releases the gas outlet opening.
This arrangement requires only a very minimal energy for actuation which is stored within the opening mechanism and which must realize only the movement of the support element. The actual opening of the different gas outlet openings is then realized by the energy of the gas which is stored in a compressed state within the storage device. In this connection, the high gas pressures effect an advantageously high acceleration of the piston system and, correlated therewith, a fast opening of the different gas outlet openings. In this connection, the peripheral wall of the storage device expediently has a tapering cross-section in the area of its end face which acts as a brake on the piston moving at high speed and thus prevents mechanical pulse peaks during the triggering process.
In a preferred embodiment, the piston(s) each have a connecting channel for pressure communication (pressure transfer) between the two partial chambers adjoining the piston, respectively; this ensures that in the rest state in all partial chambers of the cold gas generator identical pressure is present and, correlated therewith, the piston system is in force equilibrium.
In the connecting channels a flow throttle is arranged, respectively, so that, on the one hand, for the comparably slow filling of the storage device during the manufacturing process a pressure compensation in the individual partial chambers can take place while excessive differential pressures are prevented. In contrast to this, emptying of the gas stored in the individual partial chambers into the respective airbags is carried out comparatively very quickly. The flow throttles in the connecting channels avoid mutual effects of the separate airbags or of the corresponding partial chambers.
The piston rods are expediently secured in a blind bore in the area of the center axis of the respective piston wherein in the bottom of the blind bore the connecting channel is arranged approximately coaxially. In this way, with a single working step that can be automated the connecting channels as well as a receptacle for the piston rod can be manufactured; this keeps the manufacturing costs low and prevents a mechanical weakening of the piston.
Particularly in connection with tubular piston rods, these piston rods can also serve in such an arrangement as a gas line for a defined guiding of the gas flow during filling from the filling valve to the respective partial chambers. Moreover, for obtaining precisely defined flow conditions when triggering occurs, sealing of the pistons, in particular, by means of an O-ring, relative to the peripheral wall of the storage device is expedient. In this way, while providing a sufficient seal-tightness, an excellent gliding action between the piston and the peripheral wall is provided.
For simplifying the configuration, the gas outlet openings are expediently arranged in the peripheral wall such that they are covered by the correlated piston in its rest position. In this way, with simple means sealing of the gas outlet openings in the rest state as well as opening of the gas outlet openings when needed can be achieved.
Expediently, the gas outlet openings are closed by a sealing sleeve, respectively, wherein the sealing sleeve is comprised of a base body fastened on the peripheral wall of the storage device and a closure body which is connected to the piston. The base body and the closure body are connected to one another by a rated break-off location so that in the rest state, on the one hand, a reliable sealing of the interior of the storage device and, correlated therewith, maintaining of the desired pressure level for a sufficiently long duration is ensured. On the other hand, the gas outlet openings can be opened reliably and with minimal actuating forces when needed in that the respective piston, as described above, carries out a longitudinal movement and, when doing so, separates the closure body at the rated break-off location from the base body.
For this purpose, the base body is expediently configured as a circular disk on which a pin is provided as a unitary part thereof. The pin engages a correlated bore in the piston while the circular disk is fastened on the peripheral wall, in particular, by means of a sealing weld seam. Coaxially to the circular disk and the pin an outlet bore is provided whose diameter is somewhat smaller than the diameter of the pin and whose depth corresponds at least approximately to the thickness of the circular disk. In this way, in the area of the connecting location between the circular disk and the pin, a short thin-walled tube member is provided which forms the above mentioned rated break-off location. When the pin is sheared off, a precise gas outlet opening defined by the outlet bore is provided.
The desired shearing force at the rated break-off location can be simply and precisely determined by adjusting the pin diameter and the diameter of the outlet bore relative to one another. In this connection, the piston has at the side facing away from the outflow position advantageously a defined covering length relative to the outlet bore. The covering length for the individual pistons can be dimensioned differently so that, optionally, a temporal delay of the start of the inflation process of the individual airbags relative to one another can be controlled.
The filling gas is advantageously helium because this gas has a minimal dependency on pressure and temperature. In this way, the filling pressure of the storage device can be selected such that, on the one hand, at low ambient temperatures a safe filling of the airbags is possible and, on the other hand, for example, in the case of intensive solar radiation, the gas pressure does not excessively rise so that an overloading of the airbag at high temperatures is avoided. Moreover, helium has excellent flow properties which enable the connection of airbags via lines of a corresponding length to the storage device. In this way, positioning of the storage device, for example, at a suitable location in the vehicle is possible which does not coincide with the location of attachment of the airbags. Also, it is possible to fill several airbags located at different locations, when needed, with a central storage device by means of corresponding pressure lines. Moreover, an airbag filled with helium has excellent damping properties so that the impact load onto a person to be protected and particularly the HIC factor (Head Injury Criterion) can be reduced.